Basics of RTK GPS and GNSS for non-surveyors

What is RTK GPS? In fields like surveying, construction, and agriculture, precision isn’t optional—it’s essential. In many of these tasks, being off by even a few meters can lead to wasted time, costly mistakes, or failed inspections. That’s why professionals turn to high-precision positioning technologies like RTK GPS.

But to understand how RTK delivers centimeter-level results, we first need to look at the system it relies on—GNSS. GNSS provides the global coverage and satellite data that RTK builds upon. It’s the foundation of all satellite-based positioning.

Let’s start with the basics of how GNSS positioning works—and then explore how RTK takes it to the next level.

How does GNSS positioning work?

Global Navigation Satellite Systems, or GNSS, refer to satellite constellations like GPS, GLONASS, Galileo, and BeiDou. These systems provide global satellite positioning services. Many industries — from mobile navigation and logistics to construction and autonomous systems — use them in daily life.

GNSS receivers calculate their position by measuring how long it takes for signals from satellites to reach the receiver. Each signal includes data on satellite location and transmission time. When a receiver picks up signals from at least four satellites, it can determine its position on Earth.

Most standard GNSS receivers, like those in smartphones or drones, offer accuracy in the range of 2 to 4 meters. That’s fine for casual navigation, but for tasks like land surveying, construction layout, or precision agriculture, meter-level accuracy falls short.

That’s where high-precision GNSS positioning techniques like RTK come in.

What is RTK GPS?

RTK, or Real-Time Kinematic, is a positioning method that improves GNSS accuracy from meters down to centimeters. It does this by correcting satellite signal errors in real time.

An RTK system includes two GNSS receivers: a base and a rover. The base station is set at a known location and constantly receives satellite signals. It then sends corrections to the rover, which is the moving unit that needs to determine its accurate position. Because both units are observing the same satellites under nearly identical conditions, the rover can use the base’s corrections to eliminate common errors.

This method allows the rover to deliver precise position data with centimeter-level accuracy. RTK GPS technology is especially useful in surveying, mapping, agriculture, construction, and inspection tasks—where real-time precision is critical.

How RTK works?

When the rover meets the base

The base station can be a local GNSS unit or a remote reference station accessed via an RTK network. The role of the base remains the same—to provide reference data in real time that allows the rover to calculate its position with much greater accuracy.

These GNSS corrections are what make RTK stand apart from traditional GNSS. While standard GNSS relies only on signal timing, RTK takes advantage of a more detailed technique: carrier phase measurement.

Carrier phase and ambiguity resolution

GNSS signals travel as waveforms—RTK doesn’t just measure when the signal arrives, but how many full and partial wave cycles it took to get there. However, in the beginning, the receiver doesn’t know the number of whole cycles. This is called ambiguity.

RTK resolves these ambiguities by comparing signals from both base and rover. Once you resolve it, the system locks onto what’s called a FIX status—meaning the receiver has achieved centimeter-level accuracy.

This step is essential in transforming approximate GPS data into precise positioning.

Understanding RTK solution statuses

RTK solutions go through different phases as the receiver processes satellite data:

• SINGLE: No corrections are being received. Accuracy is similar to standard GNSS—several meters.
• FLOAT: Corrections have begun, but ambiguities aren’t fully resolved. Accuracy improves, but hasn’t yet reached centimeter level.
• FIX: The receiver now delivers centimeter-accurate positions after resolving ambiguities
  

Getting to FIX is the ultimate goal in any RTK setup, and maintaining FIX is key to successful high-precision work.

This video will show you how RTK technology works.

How to send RTK corrections from a base to a rover?

RTK corrections can be delivered via different channels, depending on your workflow and environment:

• Radio: Best for on-site setups without internet. It’s reliable when there’s a direct line of sight between the base and the rover.
• NTRIP: A protocol that sends corrections over the internet. Perfect for longer distances or when using a network of reference stations.
• Dual-streaming: Some systems support broadcasting over both radio and internet simultaneously. This ensures corrections stay stable even when one method becomes unreliable.

These flexible delivery methods allow users to choose the right setup for their environment—urban, rural, or remote.

What are the differences between RTK solution statuses?

RTK solutions go through different phases as the receiver processes satellite data:

• SINGLE: No corrections are being received. Accuracy is similar to standard GNSS—several meters.
• FLOAT: Corrections have begun, but ambiguities aren’t fully resolved. Accuracy improves, but hasn’t yet reached centimeter level.
• FIX: Ambiguities are resolved, and the receiver is now delivering centimeter-accurate positions.
  

Getting to FIX is the ultimate goal in any RTK setup, and maintaining FIX is key to successful high-precision work.

How to get the best RTK GPS performance in the field?

RTK depends on specific conditions to perform at its best, including but not limited to a short baseline between the base and rover, a clear view of the sky, and distance from sources of electromagnetic interference to avoid signal distortion.

Baseline

The distance between base and rover, known as the baseline, is a key factor. The closer the two units are, the more similar their satellite observations will be. Long baselines introduce environmental differences—like varying atmospheric conditions—that reduce correction effectiveness. Keeping the baseline short helps maintain the accuracy of RTK.

Satellite visibility

GNSS relies on a clear sky view. Obstacles like buildings, trees, or terrain features can block or reflect signals, weakening the quality of the data. A clear line of sight to the sky is essential for consistent fixes.

Electromagnetic interference

Electronic equipment, power lines, or heavy machinery can interfere with GNSS signals. Keeping your receiver away from such sources improves reliability and reduces signal noise.

To learn more about factors that affect signal accuracy, read our guide on eight common mistakes in GNSS surveying and how to fix them. 

Where RTK is used?

RTK GPS is now a standard tool across many industries that rely on spatial accuracy:

• Surveying and mapping: From topographic surveys to construction layout.
• Precision agriculture: Automating machinery, planting, and soil analysis with sub-inch accuracy.
• Drone mapping: Enhancing data for orthomosaics and 3D models.
• Construction: Layout tasks, volume measurement, and quality control.
• Inspection and infrastructure: Power lines, roads, pipelines, and more.

The wide range of RTK uses highlights its value in turning GNSS from a navigation tool into a precise positioning instrument. This technique transforms GNSS from a general positioning tool into a high-precision system suitable for professional tasks. RTK delivers the accuracy you need—especially when paired with the right tools, like the Emlid Reach RS3 receivers.

If you’re looking to boost efficiency, improve data quality, and unlock centimeter-level results in the field, RTK GPS is the technology to build your workflow on.

Reach RS3: ready for professional RTK

Reach RS3 makes RTK accessible and efficient for professional users. It’s a rugged, all-in-one GNSS receiver designed for high-precision work in tough field conditions.

Here’s what sets it apart:

• Centimeter-accuracy: Tracks the major GNSS constellations, including GPS, QZSS, Galileo, GLONASS, and BeiDou.
• Base and rover setup: Can be used as a stationary base or as a moving rover.
• Tilt compensation: Allows surveying even when the receiver isn’t perfectly vertical, reducing time spent leveling the pole.
• Dual-stream corrections: Supports both LoRa and NTRIP simultaneously, providing flexible connection options.
• Long-range performance: Works up to 60 km in RTK mode and 100 km in PPK workflows.
• Intuitive apps: Works seamlessly with the Emlid Flow surveying app, the Emlid Flow 360 cloud service, and the Emlid Studio post-processing software.
  

Reach RS3 supports RTK and PPK workflows, making it a powerful and versatile module for surveying and mapping.

FAQs

What’s the difference between GPS and GNSS?
GNSS includes multiple satellite systems—GPS, GLONASS, Galileo, BeiDou—while GPS refers only to the American system. GNSS offers broader coverage and better reliability.

What does RTK mean in GPS?
RTK stands for Real-Time Kinematic. It’s a technique that provides high-precision positioning by correcting GNSS signals in real time.

Can I use RTK without a base station?
Yes and no. You don’t necessarily need to own your local base station. However, you need to connect to a source of corrections data. This could be CORS or a remote reference station—you can connect to it over the internet using the NTRIP protocol.

How accurate is RTK?
With proper setup, RTK provides centimeter-level accuracy—far beyond the meter-level positioning of traditional GPS.

What happens without RTK?
Without RTK, your receiver falls back to standard GNSS, which is only meter-accurate, which may not be sufficient for your surveying tasks.